making a drivers magnet bigger: the fostex fe206e

[swak]

I have been thinking it could be possible to make a drivers magnet bigger by placing another magnet around the existing one and therefore improving (perhaps) its midrange response. This lower the Qt a little bit, give away some LF response. I would use it with the Fostexfe206e on a 250HZ front horn.

If it is worthwhile, then one (I suppose) would have to center it correctly on the existing stucture. Any comments?

[John Sheerin]

Probably not - before you go to all that trouble, you might try modeling it in FEMM to see if you'll actually gain any additional BL.

[PeteMcK]

I'm going to try this;
I have a pair of old 60's 6" 15 ohm units with a small magnet, and another pair of 8" units which have stuffed cones; they have large magnets, and the centre pole can be removed easily, and the so the magnets will fit over the magnets of the smaller units.
I'm going to bolt the frame of the larger units over the top of the smaller ones to see what effect the increased field has.
This will be an OB project...
Pete McK

[greyhorse]

I've seen one or two cases where an additional magnet was stacked on the existing one.

http://www004.upp.so-net.ne.jp/tsucchiy/jisaku5.html

Unofortunately there's no comment as to how the sound changed in this case.

[Hesky]

North Creek music, have been upgrading the magnets on the expensive high performance scan speak mid/bass drivers for many years, from the data they provide and the general comments there are it seems to work very well.

http://www.northcreekmusic.com/Drivers/Drivers.html

at the bottom of the this link you can see the modifications that are made to the drivers.

Hesky

[Variac]

Hesky,
I don't see any statement that they modify the drivers themselves. there is a model with a stacked magnet, but from what they say it could well come from the factory that way.
Am I missing something?

[Paradise_Ice]

It does help but its not that effective as it looks.
For a second magnet to be most effective it should be on the inside of the yoke plate this adds its own problems but will give a high BL.

[Nappylady]

What about field coils?

[sreten]

If the poles of the magnetic circuit are saturated are at the
gap (this is a very desirable feature) then there is no point
in simply adding more magnet, it will have very limited effect,
even if you could get the magnet inside the magnetic circuit
which generally you can't.

sreten.

[Paradise_Ice]

Originally posted by sreten
If the poles of the magnetic circuit are saturated are at the
gap (this is a very desirable feature) then there is no point
in simply adding more magnet, it will have very limited effect,
even if you could get the magnet inside the magnetic circuit
which generally you can't.

sreten.

It is possible to get 2 magnet in the circuit but its changes the BL at the top and bottom of the travel only, magnets are the most expensive part of a transducers, It is true, once the Yoke is fully saurated there is no point in adding more magnets, unless you believe it that it reduces Barkhaussen noise, if anything the magnet will suffer less reverse field modulation, but honestly i think its a fools game in general, as most speakers have fully saturated magnetic yokes, Magnets like neodymium have such a strong field they can work without a pole yoke plate, but are even better with them!